I was doing some RMAA tests and the cables were very susceptible to outside interference. Place them next to some other (power) cables and you easily see 20dB of extra noise in the measurements.Sure, it's not really a problem with short cables that you keep away from interference, but for premium/audiophile equipment I'd still expect balanced connections to be the standard by now.

With the "whole chain" I actually meant just that both the output (say, of a CD player) and the input (amp) need to be balanced for the balanced aspect to work. Perhaps redundant, but I wanted to point that out.